Physics Chapter 27
Why is the Sky Blue
-Due to selective scattering -Blue scattered light predominates in our vision. -Varies in different locations under various conditions: Clear dry day—much deeper blue sky Clear, humid day—beautiful blue sky Lots of dust particles and larger molecules than nitrogen and oxygen in the atmosphere—less blue sky with whitish appearance After heavy rainstorm (washing away of airborne particles)—deeper blue sky
Color in Our World
-Physiological experience -in the eyes of the beholder
Why is the Sky Blue
-Results of selective scattering of smaller particles than the wavelength of incident light and resonances at frequencies higher than scattered light -The tinier the particle, the higher the frequency of light it will re-emit.
Why Water Is Greenish Blue
-The intriguingly vivid blue of lakes in the Canadian Rockies is due to scattering. -The lakes are fed by runoff from melting glaciers that contain fine particles of silt, called rock flour, which remain suspended in the water. -Light scatters from these tiny particles and gives the water its eerily vivid color.
Mixing Colored Pigments
-The subtractive primary colors are cyan, yellow, and magenta. -When white light passes through overlapping sheets of these colors, light of all frequencies is blocked (subtracted) and we have black. -Where only cyan and yellow overlap, light of all frequencies except green is subtracted. -Various proportions of cyan, yellow, and magenta dyes will produce nearly any color in the spectrum.
Why Water Is Greenish Blue
-Water molecules resonate somewhat in the visible red, which causes red light to be a little more strongly absorbed in water than blue light. -Red light is reduced to one-quarter of its initial brightness by 15 meters of water. There is very little red light in the sunlight that penetrates below 30 meters of water. -When red is removed from white light, the complementary color of red remains: cyan—a bluish-green color.
Selective Reflection
-We see the color of a rose by the light it reflects
C. Yellow Light
A blue object will appear black when illuminated with A. blue light. B. cyan light. C. yellow light. D. magenta light.
D. Cyan Light
A red rose will not appear red when illuminated only with A. red light. B. orange light. C. white light. D. cyan light.
C. a mixture of particle sizes
A white sky is evidence that the atmosphere contains A. predominantly small particles. B. predominantly large particles. C. a mixture of particle sizes. D. pollutants.
Mixed Colored Light
Additive primary colors: -Red, green, and blue -Produce any color in the spectrum Red+green= Yellow Red+blue= Magenta Blue+green+red= WHite blue + green = cyan
Why Clouds are White
Clusters of various sizes of water droplets
Selective Transmission
Color of transparent objects depends on color of light it transmits -Colored glass is warmed due to the energy of absorbed light illuminating the glass
Color in Our World
Color we see depends on frequency of light -Lowest frequency, perceived as red -In between lowest and highest frequency perceived as colors of the rainbow(red, orange, yellow, green, blue, indigo, violet) -Highest frequency: perceived as violet -Beyond violet, invisible ultraviolet
Mixed Colored Light
Distribution of solar frequencies is uneven -most intense in yellow-green portion(where our eyes are most sensitive)
D. blue
If molecules in the sky scattered orange light instead of blue light, sunsets would be A. orange. B. yellow. C. green. D. blue.
Why are Sunsets Red
Light that is least scattered is light of low frequencies, which best travel through air. Red Orange Yellow
Selective Reflection
Objects reflect light of some frequencies and absorb the rest -rose petals absorb most of the light and reflect red -objects that absorb light and reflect none appear black. -objects can reflect only those frequencies present in the illuminating force.
Mixing Colored Pigments
Only three colors of ink (plus black) are used to print color photographs—(a) magenta, (b) yellow, (c) cyan, which when combined produce the colors shown in (d). The addition of black (e) produces the finished result (f).
Mixed Colored Light
Radiation curve divides into three regions that match the color receptors in our eyes
D. White Light
Red, green, and blue light overlap to form A. red light. B. green light. C. blue light. D. white light.
Why Clouds are White
Size of clusters determines scattered cloud color. Tiny clusters produce bluish clouds. -Slightly large clusters produce greenish clouds. -Larger clusters produce reddish clouds. -Overall result is white clouds. -Slightly larger clusters produce a deep gray. -Still larger clusters produce raindrops.
Mixing Colored Light
Subtractive primaries are complementary to additive primaries. Magenta, yellow, cyan -magenta + green = white = red + blue + green -yellow + blue = white = red + green + blue Example: color printing
Mixing Colored Light
Subtractive primary colors -Combination of two of the three additive primary colors Red+green= Yellow Red+blue= Magenta Blue+green+red= White blue + green = cyan
Mixing Colored Light
The shadows of the golf ball are subtractive. -Magenta (opposite of green) -Cyan (opposite of red) -Yellow (opposite of blue)
D. red and green
When the color yellow is seen on your TV screen, the phosphors being activated on the screen are A. mainly yellow. B. blue and red. C. green and yellow. D. red and green.
